Isolation, Crystallization, and Properties of Pepsin Inhibitor

A method has been described for the isolation and crystallization of swine pepsin inhibitor from swine pepsinogen. Solubility experiments and fractional recrystallization show no drift in specific activity. The reversible combination of pepsin with the inhibitor was found to obey the mass law. The inhibitor is quite specific, failing to act on other proteolytic and milk clotting enzymes. The inhibitor is destroyed by pepsin at pH 3.5. Chemical and physical studies indicate that the inhibitor is a polypeptide of approximately 5,000 molecular weight with an isoelectric point at pH 3.7. It contains arginine, tyrosine, but no tryptophane and has basic groups in its structure.